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I4                  LECTURES AND ESSAYS

is also set up. It is as if every time two bells
of a house were rung together, that of itself
made a string to tie them together, so
that when you rang one bell it was necessary
to ring the other bell in consequence. That,
remember, is purely a physical circumstance of
which we know that it happens. There is a
physical excitation or disturbance which is sent
along two different nerves, and which produces
two different disturbances in the brain, and the
effect of these two disturbances taking place
together is to make a change in the character
of the brain itself, so that when the one of them
takes place it produces the other.

Now there are two different ways in which.
a stimulus coming to the eye can be made to
move the hand. In the first place, suppose
you are copying out a book; you have the
book before you, and you read the book whilst
you are copying with your hand, and con-
sequently the light coming into your eye from
the book directs your hand to move in a certain
way. It is possible for this light impinging
upon the eye to send a message along the optic
nerve into the ganglion, and that message may
go almost, though not quite, direct to the hand,
so as to make the hand move, and that causes
the hand to describe the letter which you have
seen in the book ; or else the message may go
by a longer route which takes more time, A